Most modern ventilators offer a function, herein referred to as “oxygen boost”, which allows the operator of the ventilator to temporarily increase the oxygen concentration of the breathing gas delivered to the patient. Typically, when the operator activates the oxygen boost function, the ventilator automatically increases the fraction of delivered oxygen by a fixed amount for a fixed period of time, e.g. by having the ventilator delivering 100% oxygen instead of air for one minute of time.
However, it is difficult in clinical practice to foresee the effect of such an oxygen boost since it is difficult to know how the increase in ventilator-delivered fraction of oxygen affects the oxygen concentration in the breathing gas actually reaching the patient, at least unless monitoring said oxygen concentration by means of an oxygen sensor disposed in the proximity of the patient, e.g. in or near the Y-piece of the patient circuit connecting the patient and the ventilator.
Often, there is a considerable delay in oxygen concentration increase in the breathing gas reaching the patient. In fact, during ventilation treatment of neo-patients where tidal volumes are small compared to the volumes of hoses and additional equipment such as humidifiers, there may be a delay in delivery of increased oxygen concentration to the patient of nearly one minute, meaning that there may be no or nearly no increase in oxygen concentration in the breathing gas delivered to the patient even one minute after activation of the oxygen boost function.
Often, clinicians are mislead by the erroneous conception that activation of the oxygen boost function causes a momentary increase in oxygen concentration to a preset level (oxygen boost level), and that breathing gas with an oxygen concentration corresponding to said oxygen boost level is delivered to the patient from the activation of the oxygen boost function and for a set period of time during which the oxygen boost function is activated (oxygen boost duration).
This misconception may give rise to situations in which activation of the oxygen boost function does not have the desired effect on the ventilated patient. In some cases, for example in situations in which the oxygen boost function is activated in order to temporarily increase the patient's blood oxygen levels before disconnecting the patient from the ventilator, the unawareness of this delay may put the patient in a state of hypoxia.
US 2013/0104896 A1 discloses a medical ventilator system including oxygen boost functionality, in which the oxygen saturation level of blood in the patient is monitored during activation of the oxygen boost function. If the monitored oxygen saturation level exceeds a predetermined threshold value, the delivered oxygen concentration can be adjusted.
This functionality serves to prevent the patient from receiving too much oxygen during activation of the oxygen boost function. However, it does not prevent the patient from receiving too little oxygen. Furthermore, it requires monitoring of the oxygen saturation level of the patient's blood to realize the delayed effect of activation of the oxygen boost function.